Petrol, pipes, paint: they made a whole generation duller. That’s if you believe the research on the effects of lead on IQ. By interfering with neurological development, the lead that we used to encounter routinely has left hundreds of millions of us with a tiny bit of brain damage.
In this episode of The Studies Show, Tom and Stuart look at the toxic effects of lead - from very obvious, high-dose lead poisoning to the more insidious, low-level effects that have apparently held millions of people back. How strong is the evidence for the effects of low-level lead exposure on IQ?
The Studies Show is brought to you by Works in Progress magazine, a journal of ideas to accelerate human progress. If you’re a student aged 18-22 and want to attend the Works in Progress “Invisible College” this August (at which Stuart is speaking), take a look at this link.
Show Notes
Centers for Disease Control (CDC) page on lead poisoning
Articles on the history of lead poisoning from the BBC and the Guardian
2022 PNAS study concluding that “half of US population exposed to adverse lead levels in early childhood” (the one with the “824,097,690” figure)
Article on blood lead levels and which are considered dangerous
The 2005 meta-analysis on lead and children’s IQs
Cited in the 2021 “Global Lead Exposure Report”
The critique from the CDC in 2007
The critique paper from 2013
The critique paper from 2016
The correction from 2019
The critique paper from 2020
Quasi experiments: from Rhode Island; using manufacturing employment
2018 paper on low-level lead and all-cause mortality
Credits
The Studies Show is produced by Julian Mayers at Yada Yada Productions.
I especially enjoyed this one. I was struck by how the media, and some scientists, present the significance of a 2.5 or so IQ point effect as important and deleterious when it comes to lead, while such an effect is often dismissed as largely irrelevant when it does not fit the wider narrative of the authors/publications. See, for example, reportage around Karavani et al (2019) and similar papers pointing out the rough gains available at present through selecting embryos using GWAS acquired information: "a tiny difference" (https://www.theguardian.com/science/2021/oct/17/polygenic-screening-of-embryos-is-here-but-is-it-ethical#:~:text=A%20study%20in%202019%20suggested,picking%20the%20“best”%20embryo); "just 2.5 IQ points" (https://www.nature.com/articles/s41436-019-0744-2). I should say that the Karavani paper itself implies the same - it seems like a self-defensive measure - while stating as fact that selection for IQ would be accompanied by a higher risk of positively-correlated anorexia and autism. Of course, the authors have no idea what causes that positive correlation (again, their insistence seems more like a defensive measure against potential negative public opinion); clearly, the correlation could just as easily result from environmental conditions which affect cleverer children more so it is impossible to allocate causation in the way the authors so confidently do. At root, scientists often frame their work in a way which will not scare the horses and the media pick up the science stories they like the framing of (or where they can apply their own).
I enjoyed this episode. It was something I had no knowledge about and an example of how studies can be misinterpreted. So I was surprised when I saw a news item from the Austrlaian Broadcasting Commission about lead being sold at a chain of hardware stores across that country. See https://www.abc.net.au/news/2024-07-14/bunnings-changes-lead-products-packaging-after-concerns-raised/104094432 .
The statement is made in that article that the "World Health Organisation describes lead as one of 10 chemicals of "major public health concern" requiring action by member states – including Australia – and that there is no level of lead exposure that is known to be without harmful effects." This seems at odds with the information in this podcast.
As someone born in 1954 all I can say is my brain has been working ok. Have people got higher IQs now we have unleaded petrol?